Media Centre - IARC News

2011

HPV Vaccine Study raises Hope for Cancer Prevention

20/09/2011 -

Human papillomavirus (HPV) causes cervical cancer which is the second most common cancer in women worldwide. HPV infections also contribute to cancers of the anus, vagina, vulva, penis, and some oropharyngeal cancers.

New research on cancer-causing HPV has confirmed the vaccine's effectiveness and opened new avenues for research. The results, reported in three separate studies, suggest that vaccination programs could be less expensive than anticipated and may also have unexpected benefits.

All three studies are from an ongoing clinical trial of one vaccine, Cervarix, in Costa Rica. Their results could help develop vaccination programs to prevent cervical cancer around the world, study scientists said. In addition, they suggest that the impact of the vaccine may go beyond cervical disease.

Fewer than the prescribed three doses of Cervarix may offer as much protection as the full course, this study from the Costa Rica HPV Vaccine Trial found. If this is confirmed, vaccination could turn out to be easier to administer and more affordable, two major factors for developing countries that combine high cervix cancer rates and limited health resources.

The vaccine was highly effective for preventing persistent and potentially cancer-causing infection by HPV types 16 and 18-the most widespread and potent HPV types, targeted by Cervarix. The study also found evidence of cross-protection against other HPV strains not targeted by the original formulation-types 31, 33, and 45. While cross-protection had previously been reported, this potential benefit had not been anticipated. In addition, the study showed that, among all women vaccinated, the Cervarix vaccine is more efficacious among women 18-19 years old than among those 24-25.

Protection from fewer doses, and wider protection that anticipated

The discovery that two doses -and possibly even one- of Cervarix may protect against infection was made possible because the study was conducted in a community setting. Approximately 20 percent of the women in the trial received only one or two doses, often because of pregnancy or an unrelated health problem.

The scientists found that all of the women who received the vaccine were protected equally regardless of the number of doses received -at least for the first 4 years after vaccination. At the end of 4 years, the scientists offered the vaccine to women in the control group, and all participants will be followed to determine how long the protection lasts and whether cross-protection is long-lasting.

If these important results are confirmed, they could have implications in terms of public health measures. For one, the cost of immunization programs could drop. If countries can afford to vaccinate only certain groups, they need to know which ones would benefit most, and this group would likely be young women who are not yet sexually active, as exposure to HPV weakens the effectiveness of immunization, once sexual activity starts.

Furthermore, the study reported for the first time efficacy of the vaccine against anal HPV infection in women, with potential implications for the prevention of anal cancer, an effect likely to benefit both men and women.

A number of issues remain unanswered, however: how long one or two doses of the vaccine keep protecting against HPV infection is not known. These findings might also not apply to other vaccines or to other populations, such as people who are malnourished or lack strong immune responses.